One of the only ways to do this, is having everything stored in a fully documented format. For photos, I don't think much exist except the most naive raw format

One of the only ways to do this, is having everything stored in a fully documented format. For photos, I don't think much exist except the most naive raw format (think bitmap files, just in same colour space as NEF or the like), accompanied with an XML/JSON file with the metadata and a document describing this. Once it is needed, you have to convert it. Sounds about right you could build a business on that idea - first step is to find someone willing to pay for it though.